Magnetic disk devices used in mainframe computers, workstations, personal computers, and the like have become more important year by year, and have been improved in capacity increase and size reduction. For increased capacity and size reduction in those magnetic disk devices, higher density is crucial. One of such techniques for attaining higher density is reduction in media noise by a smaller unit of magnetization reversal in magnetic recording media. To that end, conventional magnetic recording media have adopted a configuration in which ferromagnetic crystal grains comprising a magnetic recording layer are preliminarily separated by a nonmagnetic material contained in the magnetic recording layer.
Today, to control separators more actively to improve magnetic recording density, discrete track media (DTMs) in which recording tracks are separated, and further, bit patterned media (BPMs) in which recording bits are separated, have been researched and developed. In both of these media, the processing technology to form the separators is a significant point for higher recording density.
As a method for producing a DTM, the magnetic layer processing type has been proposed that physically processes magnetic films by etching, for example. The magnetic film processed DTM are typically produced by the following processes:    (1) Provide a metal thin film on a recording medium and applying resist on top of it.    (2) Form a fine pattern on the resist according to the lithography technology.    (3) Etch the metallic thin film in concave part of the resist pattern by a dry etching process to expose a recording layer.    (4) Etch the exposed recording layer by a dry etching process to form recording track separators (grooves).    (5) Remove residual resist and the metallic thin film on recording tracks (lands).    (6) Backfill the grooves with a nonmagnetic material to planarize them.    (7) Provide a protection layer and a lubricant layer.
In this way, in production of the magnetic layer processed DTMs, process steps are very complicated, and further, the backfilled and planarized surfaces are rougher than those of continuous media, which disadvantageously causes unstable flying performance of magnetic heads.
For another method of producing DTMs to overcome the above problem, a technique has been proposed that demagnetizes grooves by ion implantation. According to Japanese Patent Publication No. 2007-226862, a fine pattern is placed on a magnetic recording medium formed up to a protection layer, and ions of Si, In, B, P, C, and F are implanted by a commercially available ion implanter. According to Japanese Patent Publication No. 2006-309841, DTMs can be produced by implanting ions of Ag, B, Cr, Mo, Al, Nb, or the like through a stencil mask. According to Japanese Patent Application Publication No. 2007-220164, a method of producing DTMs is disclosed that deposits Si on a fine processed concave part of a resist and selectively diffuses the Si in the pre-groove area on the recording layer. According to these disclosures, the manufacturing methods are simpler than that of the magnetic film processed DTMs and the flying performance of a magnetic head is better because of the smoothness of the surfaces of the prepared media.
Production of DTMs by ion implantation, however, has a problem of increased volume of the implanted part. That is, the part where the element ratio of a ferromagnetic material was relatively reduced by ion implantation increases in volume to cause increase in height compared with the non-implanted part. Thus, it may cause increase in distance between the non-implanted part corresponding to the magnetic recording tracks and the magnetic head. Consequently, the increase in spacing loss may interfere with higher recording density.
For example, when the recording layer made of a Co alloy having a thickness of 20 nm, there exist approximately 1017 atoms per cm2. When Cr ions of 1016 atoms are implanted for the purpose of deterioration in magnetic characteristics, the volume increases by 10% if the density remains relatively constant. The implanted ions spread in the in-plane direction within the magnetic layer so that the height increases as a whole, but the height in the implanted part increases more than the non-implanted part so that the distance from the magnetic head in the non-implanted part (magnetic recording tracks) becomes longer than in the implanted part. To reduce the medium noise in read and write operations by a magnetic head, it is more advantageous if the difference in magnetic characteristics between the implanted part and the non-implanted part is larger. On the contrary, increase in dose for this purpose causes a notable increase in volume to disadvantageously increase the spacing loss.